1. Field of the Invention
The present invention relates to a transformer, and more particularly to a transformer with good insulation.
2. Description of the Related Art
Generally, because the secondary side of a transformer has a high voltage, it is generally necessary to insulate the secondary winding to prevent the electric elements or users from being harmed by high voltage. However, there are many shortcomings to several conventional method of insulating the secondary winding.
A conventional transformer, as shown in FIG. 1a, is composed of a bobbin 10a, a core structure and an insulating shell 30. The core structure comprises two E type cores 50 which are coupled together by being inserted into the two ends of the bobbin 10a respectively. The bobbin has a primary side 20a and a secondary side 20b. The primary side 20a is provided with a primary winding (not shown) and the secondary side 20b is provided with a secondary winding (not shown). The primary side 20a is separated from the secondary side 20b by a first separating flange 25. In addition, the primary winding is electrically coupled to at least one of the primary pins 21, and the second winding is electrically coupled to at least one of the secondary pins 22. The secondary side 20b further comprises a plurality of secondary flanges 27 for producing several dividing voltages. Namely, the primary winding and the secondary winding are formed along the same axis of one bobbin. Moreover, the transformer further comprises an insulating shell 30 to insulate the secondary winding from outside. The insulating shell 30 encloses the whole bobbin 10a. 
However, in the conventional transformer shown in FIG. 1a, because only the first flange 25 is used to insulate the secondary winding from the primary winding, the primary winding is not completely insulated from the secondary winding. The creepage distance between the primary winding and the secondary winding may be not enough when the primary winding and the secondary winding are formed at the primary side 20a and the secondary side respectively, due to poor design or error in the production process, for example, the first flange 25 is too low or the secondary winding is wound too thick. In this case, the high voltage at the secondary winding may be short-circuited to the primary winding, thereby decreasing the efficiency of the transformer.
Another conventional method is to insulate the secondary winding by using an insulating glue. In FIG. 1b, a conventional transformer with an insulating glue is comprised of a bobbin 10b, a core structure and a container 60. The core structure comprises two E type cores 50 which are coupled together by being inserted into the two ends of the bobbin 10a respectively. The bobbin 100 has a primary side 20a and a secondary side 20b. The primary side 20a is provided with a primary winding (not shown) and the secondary side 20b is provided with a secondary winding (not shown). The primary side 20a is separated from the secondary side 20b by a first separating flange 25. In addition, the primary winding is electrically coupled to a least one of the primary pins 21, and the second winding is electrically coupled to a least one of the secondary pins 22. The secondary side 20b further comprises a plurality of second flanges 27 to produce several dividing voltages. Namely, the primary winding and the secondary winding are along the same axis direction of one bobbin. The transformer further comprises a container 60 to hold the secondary winding from the environment. The container 60 is used to include the bobbin 10b and the core structure. The insulating glue is added into the container 60 to insulate the secondary winding from environment.
However, the transformer shown in FIG. 1b not only has the problem about creepage distance, but it is also difficult to implement the transformer in the Surface Mount Device (SMD) type. Instead, the transformer must be implemented in stitch type because the bobbin 10b must be placed in the container 60. However, it is very difficult to control the potting height to cover the bobbin 10b but still expose the pins 21 and 22 because the pins 21 and 22 in the transformer of the SMD type and the lower surface of the bobbin 100 are almost in the same plane. Furthermore, the insulating glue must be added in a vacuum environment to prevent bubbles from being formed when the insulating glue is added into the container 60.
In view of this, it is desirable to develop a novel transformer to solve the problems mentioned above.
An object of the present invention is to provide a transformer wherein the high voltage side (secondary side) is insulated completely. The transformer of the present invention comprises a bobbin, an insulating shell and a core structure. The surface of the bobbin is provided with a plurality of flanges, a plurality of secondary side pins and secondary winding. The flanges are formed on the surface of the bobbin to form a plurality of slots on the surface of the bobbin. A conductive wire is wound on those slots to form the secondary winding. The secondary winding is electrically coupled to the pins.
The insulating shell is comprised of an upper insulating cover and a lower insulating cover, wherein the upper insulating cover covers the top surface of the bobbin and the lower insulating cover covers the bottom surface of the bobbin. Namely, the secondary winding and surface thereof are enclosed by the upper insulating cover and the lower insulating cover. Consequently, the secondary winding of the bobbin is completely electrical insulated from the environment. Moreover, another conductive wire is wound on the insulating shell to server as the primary winding and electrically coupled to the primary pins.
The upper insulating cover further comprises a top extending board, and the lower insulating cover further comprises a bottom extending board. The top extending board and the bottom extending board extend beyond the secondary pins. Alternatively, the top extending board and the bottom extending board enclose the secondary pins exactly.